Just heard something disturbing...need help!?

Okay this is a bit long, so i'll try to shorten it. I posted a few days ago that my 2 bros were doing Roxie's- a RX med thats basically synthetic heroin, which will make sense in a min. My youngest sis is for lack of a better word, a whore. I found out yesterday that she slept with 16 guys- (She's 16 yrs. old ) including our middle sis's Husband, HIS sisters H, my best friends H, and at least two other family friends. Now, she and our mid. Sis used to be close, so they told each other everything (obviously, before she screwed her H) This is were the story gets sick. Lil sis claims that she actually slept with one of her/our older brothers while they were messed up on pills. I'm sick even thinking about that, and I don't know what to do. I don't know if she's lying for attention, ( warped, I know) or if it really did happen, but I think there is something wrong in that girls head. Question is- what do I do? tell my rents, confront her, confront our bro, turn them into Jerry Springer?? I am so confused right now, I don't know what to do. Any advice on how to get to the bottom of this, and how to handle it would be greatly appreciated. and to any naysayers, I'm 100% serious- this is what I was told yesterday after learning my older bros were drug users: my mid. sis told me the whole story because at first, she thought lil' sis was lying, but knowing now that he gets trashed on pills, it doesn't seem out of the realm of possibility. She felt like she needed to tell someone, it was making her sick keeping it to herself. Again, any advice would help!